This application is based on patent application Nos. 9-244415, 9-244416, 9-244417 filed in Japan, the contents of which is hereby incorporated by reference.
This invention relates to an apparatus capable of shake estimation to correct a displacement of an object light image caused by a shake of the apparatus relative to an object.
In recent years, there have been marketed video cameras and electronic still cameras having a function of shake correction. In such a camera, a CCD (Charge Coupled Device) detects a shake amount of an optical image pickup system relative to an object due to a camera shake, and a shake correction is performed in such a manner as to cancel the shake amount. This shake correcting function is also applied to usual halide film cameras.
Japanese Unexamined Patent Publication No. 8-51566 discloses a camera with a shake correcting function as follows. A solid state image sensor such as CCD is provided to pick up an object light image for detecting a shake amount. An estimative shake amount is calculated considering time required from start of shake detection to completion of driving of a shake correction optical system to cancel the detected shake amount, including time for the calculation of estimative shake amount and driving the optical system. The shake correction optical system is driven based on the calculated estimative shake amount.
Further, various correction manners for estimation of a moving object to ensure an optimum focusing control have been proposed.
U.S. Pat. No. 4,998,124 discloses a manner of narrowing the distribution of focus detection results to multiply a speed of a moving object by a coefficient xc2xd.
U.S. Pat. No. 4,998,124 further proposes an object speed calculation for a moving object follow-up mode when executing auto-focusing. In this calculation, an estimative speed is obtained by averaging an instant defocus amount and a defocus amount prior to the instant defocus amount, and multiplying the average by xc2xd. Also, this publication discloses an average estimative mode wherein if latest three focusings are failed, and the respective directions of latest two detection data do not coincide with each other, an average of the latest three detection data is calculated as defocus data.
U.S. Pat. No. 4,908,645 discloses a calculation using an analogous quadratic function. Specifically, an estimative moved amount of an moving object is calculated using three detection data for auto-focusing in the case where the moved amount of the object is large. The coefficient for the quadratic function is changed in accordance with detection intervals.
U.S. Pat. No. 5,327,190 proposes a manner of providing a linear correction function and a quadratic correction function to correct the focusing speed. The correction functions are switchable over. In the linear function, a moving speed is multiplied by a coefficient. In the quadratic function, a moving speed is squared, and the squared speed is multiplied by a coefficient.
U.S. Pat. No. 5,138,356 discloses a calculation of an estimative speed of a moving ofject. Three moving speeds are calculated based on latest five defocus amounts. These moving speeds are averaged to obtain a provisional estimative speed. Further, an average of four provisional estimative speeds is calculated, and applied to an analogous quadratic function to obtain a final estimative speed.
U.S. Pat. No. 4,783,677 proposes a calculation for a moving object follow-up mode. In this calculation, an estimative speed is obtained by calculating an average of a series of defocus data while adding latest data with more weight.
Japanese Unexamined Patent Publication No. 60-214325 discloses an auto-focusing device comprising a defocus amount detector for detecting a defocus amount and an object movement detector for detecting a moved amount of an object based on a detection result by the defocus amount detector. Detected defocus amount is corrected on time basis using a detection output of the object movement detector to drive a focusing lens based on a corrected defocus amount. In this publication, the defocus amount at an intermediate point of an integration time is obtained by calculating an average of adjacent two defocus amounts, irrespective of calculation of the moved amount of the object.
However, such estimation of a moving object cannot be applied to calculation of an estimative shake amount. It could be appreciated to calculate an estimative shake amount using a quadratic function on the assumption that a camera shake is a uniformly accelerated motion. This can provide a precise estimation at a very instant moment. However, for calculation of an estimative shake amount, attention must be paid to the fact that the acceleration of camera shake varies at all the time, although the shake range is not actually so large. In the period from start of shake detection to completion of shake correction, there is a likelihood that a calculated estimative shake amount becomes void, causing an imperfect correction.
It is an object of the present invention to provide an apparatus capable of shake estimation which has overcome the problems residing in the prior art.
According to an aspect of the invention, an apparatus comprises: a detector which detects a shake amount of the apparatus with respect to an object at an interval; a calculator which calculates a shake speed and a shake acceleration rate based on detected shake amounts, and calculates an estimative shake amount based on a calculated shake speed, a calculated shake acceleration rate, and a coefficient k (0 less than k less than 1) on an assumption that a shake is uniformly accelerated motion, the coefficient k being a multiplier for the calculated shake acceleration rate; and a corrector which executes a shake correction in accordance with a calculated estimative shake amount.
According to another aspect of the invention, an apparatus comprises: a detector which detects a shake amount of the apparatus with respect to an object at an interval; a selector which selects, in accordance with a predetermined reference time space before a particular detection time point, a plurality of shake amounts among shake amounts detected by the detector; and a calculator which executes calculation on a shake of the apparatus based on detected shake amounts selected by the selector.
According to still another aspect of the invention, an apparatus comprises: a detector which detects a shake amount of the apparatus with respect to an object at an interval; and a calculator which calculates an average shake amount of a plurality of shake amounts continuously detected by the detector.